Synthesis and Characterization of Imino‐Phenolate Titanium Complexes and Their Use in Homo‐ and Copolymerization of Ethylene

Abstract

A set of titanium precatalysts [(L)TiCl3] based on imino‐phenolate tridentate ligands (Ti1, L = 3,5‐tBu‐2‐(OH)C6H2CH‐N‐8‐C9H6N; Ti2, L = 3,5‐tBu‐2‐(OH)C6H2CH‐N‐C2H4‐O‐C6H5; Ti3, L = 3,5‐tBu‐2‐(OH)C6H2CH‐N‐CH2‐C6H4OMe; Ti4, L = 3,5‐tBu‐2‐(OH)C6H2CH‐N‐C6H4‐C6H5O) is prepared and characterized by elemental analysis, IR, and NMR spectroscopy. Upon activation with methylaluminoxane (MAO), these precatalysts show good activity (200–660 kg of PE mol[Ti]−1 h−1 at 60 °C) in ethylene polymerization yielding high‐density poly­ethylenes (HDPEs) with viscosity‐average molecular weight (Mv) in the range between 184 and 355 × 103 g mol−1. The Mv values of the resulting polyethylenes indicate strong influence of the aluminum concentration on the molecular weight, which can be associated to the probability of chain transfer from titanium to aluminum at high [Al]/[Ti] molar ratios. The polydispersity index (PDI) calculated from Gc(ωc) values are broad (24 to >40) indicating the multisite nature of this class of titanium precatalysts. Ti1–Ti4 are also tested in the copolymerization of ethylene with 1‐hexene affording high‐molecular‐weight poly(ethylene‐co‐1‐hexenes) with comonomer incorporation varying from 1.0 to 4.1 mol%. The crystallization analysis fractionation (CRYSTAF) profiles of copolymers produced by Ti2–Ti3 indicate the production of HDPE with very low efficiency (quantity and distribution) on incorporating 1‐hexene. On the other hand, the polymer produced by Ti1 shows a broad peak of branching fraction with different amount and comonomer distribution, suggesting a good 1‐hexene distribution along of main polymer chain. image